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jasper,opaque, impure cryptocrystalline quartzquartz,
one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2.
..... Click the link for more information. , usually red, but also yellow, green, and grayish blue. It is used as a gem. Ribbon jasper has the colors in stripes.
Jasper,city (1990 pop. 13,553), seat of Walker co., NW central Ala.; inc. 1889. Jasper is a trade and processing center in a coal and timber area. There is agriculture and the manufacture of sporting goods and furniture, as well as bottling and poultry processing.
a compact, fine-grained rock, composed mainly of quartz, chalcedony, and colored impurities of other minerals, such as hematite, goethite, manganese hydroxides, chlorite, and actinolite. Jasper is one of the most common and most beautiful gems.
On the basis of composition, jaspers are subdivided into essentially quartz jaspers proper, quartz-chalcedonic jasperoids, and feldspar-quartz jasper-like rocks. They are characterized by good hardness (5.5–7.0 on Mohs’ scale), strength, a large variety of colors, and the capacity to acquire a high polish. Various shades of red, green, yellow, and gray predominate; red-brown, black, and white are encountered less frequently. Jaspers are opaque and exhibit a conchoidal fracture. On the basis of texture, they are subdivided into solid, monocolored jasper, striped jasper, multicolored jasper, with colored veins and spots, and spheroidal, or “penny,” jasper. Landscape jasper, a type of multicolored jasper, is especially valuable. Jaspers are deposited in the form of layers, lenses, and strata measuring tens or hundreds of meters in thickness.
Jaspers are polygenous formations. Jasper proper is most often metamorphosed siliceous radiolarian ooze and argillaceous siliceous deposits genetically linked to greenstone effusive rocks and tuffs of spilite-keratophyre formations (for example, the Southern Urals deposits at Kalkan and the Orsk group with Mount Polkovnik, composed of landscape jasper). Jasper-like hornblendes and other jasper-like rocks were formed in the course of contact metamorphosis or silicification of various shales and effusive rocks (for example, the Revnevskoe and Gol’tsovoe deposits and the Leninogorsk group in the Rudnyi Altai). Outside the USSR, jasper deposits are found in the USA, India, and Venezuela.
Jasper has long been used for making fine objects, such as cylindrical seals, jewelry, and amulets, and Florentine mosaics and other interior decorations, such as vases, fireplaces, and columns. It is currently used in fine crafts, jewelry, and the manufacture of mortars, knife-edge bearings, and step bearings.
REFERENCEKievlenko, E. la., and N. N. Senkevich. Geologiia meslorozhdenii podelochnykh kamnei. Moscow, 1976.
T. B. ZDORIK